1. Field of the Invention
The present invention relates to a method of and apparatus for automatic equalizing filter in a time division multiple access system for use in a digital mobile communication system, such as mobile telephone or the like.
2. Description of the Related Art
In the U.S.A., European countries and Japan, mobile telephone systems that are a kind of mobile communication systems have hitherto been digitized. It is known that this digital mobile telephone system uses a time division multiple access (TDMA) system.
In European countries, there is used a GSM (group special mobile) system that is a kind of TDMA systems.
In this GSM system, a communication channel from a base station to a mobile station (automobile) has a frame format shown in FIG. 1A. As shown in FIG. 1A, 8 time slots, each being formed of 156.25 bits, constitute a unit frame of 1250 bits which correspond to 4,615 msec.
One time slot is formed of a sync. (synchronizing) data portion of 26 bits disposed at substantially the center of one slot and digital data portions of 58 bits disposed ahead of and behind the sync. data portion or the like as shown in FIG. 1B.
In the GSM system, there are designated in advance 8 kinds of data sequences as the sync. pattern of this sync. data portion. FIG. 1C shows one of such 8 data sequences.
In the mobile communication system, such as the mobile telephone or the like, it is frequently observed that a tall building or the like is interposed between a mobile station moving at high speed and a base station. In this case, the mobile communication system is easily affected by a so-called multipath. When the mobile communication system is affected by the multipath, there occur intersymbol interference and interchannel interference, thereby deteriorating a transmission characteristic between the base station and the mobile station considerably. Therefore, it becomes impossible to receive a transmitted communication with small transmission error. In addition, this equivalent transmission characteristic fluctuates from hour to hour.
In such mobile communication system, the use of an equalizer becomes indispensable for minimizing transmission errors. In this case, tap coefficients of a digital filter that constructs this equalizer must be determined at high speed with high accuracy. Further, the transmission with small transmission error should preferably be implemented using simple hardware or using minimal computations as possible or with a calculation amount as small as possible.